Two-package urethane coatings produced by reacting an organic polyol with an organic polyisocyanate or an isocyanato terminated prepolymer are known in the art. In many instances, it is desired to have a pigmented two-package urethane coating wherein the pigment is dispersed in the polyol package prior to the application of the coating. Usually, the pigment is dispersed in the polyol package by the use of high shear mixing equipment such as a three roll mill, sand mill or Cowles type mixer. A problem has been observed in certain of these polyol-dispersed pigmented two-package urethane coatings in that the pigment particles tend to flocculate when the pigmented polyol package contacts the polyisocyanate or isocyanato terminated prepolymer package. The resultant poor pigment dispersion in the applied coating impairs the physical properties of the coating, such as gloss, weatherability, hardness, abrasion resistance and chemical resistance. The flocculation problem is particularly severe when pigments are used which are initially difficult to disperse in the polyol package, for example, titanium dioxide. The degree to which pigment flocculation occurs is also believed to be partially dpendent on the pigment wetting characteristics of the particular organic polyol and organic polyisocyanate used in the two-package urethane coating. As a result of pigment flocculation, many pigmented two-package urethane coatings do not exhibit the same degree of gloss, weatherability and physical properties which they exhibit in unpigmented form.
Previous efforts to overcome pigment flocculation have been directed primarily toward stabilizing the pigment dispersion in the polyol package by the use of surface active dispersing agents, which are known in the art. These include the anionic, cationic, electro-neutral, amphoteric and non-ionic surface active dispersing agents. None of these methods has been completely successful.